# Migration Guide

This repository uses Parquet-only HuggingFace dataset branches for Universal
Dependencies releases. Current examples use the official dataset location:
`universal-dependencies/universal_dependencies`.

## v2.2.x to v2.3.0

Loader/framework v2.3.0 updates the generated Parquet schema for regular CoNLL-U
token fields:

- `upos` is now stored as a list of strings instead of HuggingFace `ClassLabel`
  indices.
- `head` is now stored as a list of 16-bit integers instead of strings.
- Empty-node `head` values remain strings because CoNLL-U empty nodes may use
  `_` for HEAD.

### What Usually Changes

Most users can load and iterate over datasets as before:

```python
from datasets import load_dataset

ds = load_dataset(
    "universal-dependencies/universal_dependencies",
    "en_ewt",
    revision="2.18",
    split="train",
)
```

Code that expected `upos` as integer class IDs should now work directly with
strings:

```python
upos = ds[0]["upos"]
assert upos[0] == "PROPN"
```

Code that compared `head` to strings should compare to integers:

```python
heads = ds[0]["head"]
root_positions = [i for i, head in enumerate(heads) if head == 0]
```

If you need string output for CoNLL-U serialization, convert at the boundary or
use the helper package:

```python
from ud_hf_parquet_tools import write_conllu

write_conllu(ds, "output.conllu")
```

### Compatibility Notes

`ud-hf-parquet-tools>=1.3.0` can still reconstruct older Parquet outputs where
`upos` was stored as a `ClassLabel`. New outputs should use the v2.3.0 schema.

## Archived v1.x to v2.0 Notes

The v1 loader used a Python dataset script and required `trust_remote_code=True`.
The v2 line removed the script loader and distributes Parquet files directly,
which requires `datasets>=4.0.0`.

Important v2.0 data changes:

- Multi-word token surface forms are no longer included in regular `tokens`.
- Multi-word token information is preserved in the structured `mwt` field.
- Helper functions moved out of the dataset repository and into
  `ud-hf-parquet-tools`.

Old v1 code like this:

```python
dataset = load_dataset(
    "universal-dependencies/universal_dependencies",
    "fr_gsd",
    trust_remote_code=True,
    revision="v1.0",
)
```

should be replaced with current Parquet loading:

```python
dataset = load_dataset(
    "universal-dependencies/universal_dependencies",
    "fr_gsd",
    revision="2.18",
)
```

For token-count checks, use `num_words` from `metadata.json` rather than
`num_tokens` when comparing against regular syntactic-word sequences.

## Repository Move

The dataset was formerly maintained at `commul/universal_dependencies` and now
lives under the official Universal Dependencies organization at
`universal-dependencies/universal_dependencies`:
https://huggingface.co/datasets/universal-dependencies/universal_dependencies

## Support

- Changelog: [CHANGELOG.md](CHANGELOG.md)
- Dataset repository: https://huggingface.co/datasets/universal-dependencies/universal_dependencies
- Helper library: https://github.com/bot-zen/ud-hf-parquet-tools
- Discussions: https://huggingface.co/datasets/universal-dependencies/universal_dependencies/discussions